Process for treating windshields of organic glass and, respectively, the outer layers thereof

ABSTRACT

An airplane windshield in the cockpit made of organic glass provided with a reliably effective antistatic coating which can withstand any external influences on a permanent basis and for preventing static charges under adverse weather and flight conditions, having its surfaces treated with bromine vapor, diluted bromine solution and/or other halogens.

I United States Patent 115] 3,647,5 1 5 Hahn 1 1 Mar. 7, 1972 [54] PROCESS FOR TREATING 3,485,574 12/1969 Miller et a1. ..117/1388 2,876,185 3/1959 Wolinski ..l I7/47 g;% R, GLASS 2,801,447 8/1957 Wolinski ..1 17/ 138.8 AN 1 OUTER 2,832,697 4/1958 Walles 117/62.1 LAYERS THEREOF 3,036,930 5/1962 Grimminger et al. 1 171138.11 2,788,306 4/1957 Cox et ..117/62.l [72] g' 3,364,056 l/1968 Seibel 117/1388 "many 3,076,124 l/1963 Viscardi. 17147 [73] Assignee; Hamburger Fluguugbgu Gmbfl 2,832,698 4/1958 wallcs 117/621 2,805,960 9/1957 Wolinski l7/47 [221 1968 2,727,831 12/1955 Dixon et a1. ..117/62.|

21 A LN 763818 1 pp 0 Primary Examiner-William 1). Martin Assistant Examiner-M. Sofocleous [301 Foreign Application Priority Data Attorney-Otto John Munz Sept. 29, 1967 Germany ..P 16 94 393.4 [57] ABSTRACT [52] U.S.Cl. ............................117/62, 117/106 R, 117/118, An airplane windshield in the cockpit made of organic glass 117/1383 R provided with a reliably effective antistatic coating which can [51] lnt.Cl. l/18,B44d 5/12 wi h tan ny ext rn l infl nc n a perm nent basis an 158] Field of Search..... ...,1 17/47 R, 133,8 5, 62 62,]. for preventing static charges under adverse weather and flight 117/63, 106, 118; 156/2; 252/79 conditions, having its surfaces treated with bromine vapor,

diluted bromine solution and/or other halogens.

[56] References Cited 60mm, 7 Dr. I g

UNITED STATES PATENTS Fortner et a1 [71138.8

PAIENTEDMAR 7 m2 3,647, 515

sum 1 OF 5 Inventor- .lANS-Il WRCiN HAHN Al HJRNI'Y PATENTED MAR 7 I972 SHEET 2 BF 5 INVENTOR.

HANSHHIRGhN HAHN wGE PATENTEDHAR 7 I972 3.647, 515

SHEET 5 BF 5 A ORTJEY PROCESS FOR TREATING WINDSIIIELDS OF ORGANIC GLASS AND, RESPECTIVELY, THE OUTER LAYERS THEREOF BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for treating windshields made of organic glass and, respectively, the outer layers thereof, particularly the windshields of airplanes and aircraft with halogens in vapor or solutions to prevent the formation of static changes.

2. Description of the Prior Art For safety reasons, for example in order to assure stability against large numbers of birds in flight, the cockpits of modern airplanes are equipped with windshields made of organic glass. Under certain weather and flight conditions, a static charge is formed on these windshields. When this electric charge has reached a specific level, a visible discharge takes place which, as experience has shown, may be transferred to the electrical wiring system of the airplane, resulting in breakdowns of instruments and generators. In such a case, the pilot can no longer safely steer the airplane and particularly a safe landing of a plane havingjet propulsion drive is seriously questioned.

Already known in the art are several processes with the aid of which a certain antistatic property on the surfaces of plastic windshields may be obtained. For example, antistatic lacquers may be applied, or the surfaces of the plastic windshields may be coated with antistatic liquids. It is further known to evaporate electrically conducting layers thereon. The electrically conducting layers which are produced with the known processes are, however, not sufficiently resistant to wiping, they are not resistant against rain erosion, partially inadequately resistant against ultraviolet radiation, and too sensitive to heat. In order to obviate these difficulties, attempts to render plastics antistatic have previously been made by adding suitable antistatic agents to the mixture during the manufacture of the windshield material. The efficacy of such admixtures is limited because the specific resistance of the windshields can be reduced only by about two tenths powers. Lastly, also the optical properties of the windshields which have been treated in accordance with the aforementioned processes leave much to be desired so that the antistatic treatment of the windshields of airplanes and aircraft which is carried out on the basis of the prior art processes is not found to be satisfactory for the purpose of preventing electric charges thereon.

Moreover, experiments with acid treatments have been carried out as well; for example, chlorosulfonic acid whose action on plastic surfaces is sufficiently known has been employed for this purpose. During these experiments, concentrated nitric acid as well as sulfuric acid were also tested. While the acid treatments resulted initially in a good antistatic effect on the plastic surfaces, the stability thereof was rather limited. It has been found that the antistatic property disappears again to a large extent after several days due to the action of heat and humidity.

SUMMARY OF THE INVENTION The objects of the invention are:

To eliminate the aforementioned difficulties and drawbacks of the prior art processes for treating windshields of organic glass and, respectively, the outer layers thereof, particularly the windshields of airplanes and aircraft; to reduce the usual high specific electric resistance of the surface of a windshield, which when made of organic glass is generally from to 10" ohm X centimeter, to approximately 10 ohm X centimeter, to make the surface of the windshield electrically conducting and thus to achieve the desired antistatic effect thereon; to provide a reliably effective antistatic coating which can permanently withstand any external influences and which prevents that the windshields of airplanes or aircraft be statically charged; to treat the surfaces of the windshields with either bromine vapor or a diluted bromine solution and,

respectively, with other halogens; to change permanently by virtue of the use of the process of the invention the plastic antistatically at the surface thereof up to a depth of I50 pt; to obtain a permanent chemical change of the macromolecules by adding bromine or equivalents and compositions thereof to the double bonds in the plastic.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the accompanying drawings and description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. I to 3 are cross-sectional views on an enlarged scale of panes of the glasses described.

FIGS. I and 2 are cross-sectional views of the glasses treated in accordance with the prior art, and are presented here for purposes of comparison,

FIG. 3 is a view of glass treated in accordance with the present invention;

FIGS. 4 and 5 are diagrammatic views showing certain relationships resulting from the processes of the present invention;

FIG. 6 is a table showing results of treatment carried out in accordance with the present invention; and

FIG. 7 is a perspective view of an apparatus for performing the process of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The specific electric resistance of a windshield made of organic glass is generally from 10 to 10 ohm X centimeter.

To prevent that the windshields be electrically charged, therefore the surfaces thereof must be made electrically conducting, i.e., antistatic. In order to achieve the required antistatic effcct on the windshields, it is necessary to reduce this high specific resistance to approximately 10 ohm X centimeter.

in accordance with the invention the desired results are accomplished by treating the surfaces of the windshields with materials which are compatible with the plastic glass material on hand, readily adhere thereto and do not affect adversely its light transmission and have the desired conductivity. The inventor discovered that among the numerous materials best suitable for this purpose are halogens, namely, chlorine, bromine, fluorine and iodine. The first two mentioned halogens are particularly best suitable for the purpose.

The electrical conductivities of these substances of a centimeter cube, that is their conductance expresed in mhos per centimeter, given by the ratio of the current density to the applied electric field, are known.

This affords the possibility of adapting the process of the present invention to the respectively required degree of conductivity of the antistatic coating of the windshield surfaces.

The inventor found that the conventionally used windshields made of organic glass generally have a specific resistance from 10' to 10" ohm X centimeter and that in order to achieve the desired antistatic effect on the windshield, it is necessary to reduce this high specific resistance to approximately l0 ohm X centimeter. Thus it remains only a matter of determination of the specific resistance of the actual windshield glass on hand to impart to it by the method of the present invention the desired conductivity by providing it with a specific or a mixture of halogens, the conductivity or conductivities of which are predetermined.

According to the present invention, the reaction may be accelerated by means of light or heat.

The accompanying drawings illustrate three cross-sectional views at an enlarged scale through parts of windshields l, 2, 3 with treated surfaces 4, 5, 6. FIGS. 1 and 2 show the chemical effect of the treatment in depths of penetration 7, 8 respectively, up to u, as they are produced with the aforementioned processes which are not suitable for airplanes and aircraft. FIG. 3 illustrates a part of a windshield surface which has been chemically treated according to the present invention with a depth of penetration of from 9 to l00 u.

The diagram of FIG. 4 shows the relationship between the surface resistance and the time of bromine action at four differently chosen temperatures. The percentage of halogens. particularly bromine and iodine, is produced as a function of the temperature on the basis of the vapor pressure equilibrium in accordance with Henry's Law. The temperatures and durations of treatment are apparent from the following table. They depend upon the material that is to be treated.

TABLE Surface Resistance (Ohm)=-;f (Bromine action h) at and C.

Surface Resistance (Ohm) The surface resistances obtained as a function of time and temperature can be read on the abscissa of the diagram. The curves shown refer here to a specific material, namely, to a polymer having the base of allyl diglycol carbonates only because this material is preferred in the art as a scratch-resistant surface layer for glazing airplanes.

In the diagram of FIG. 6 pure transmission =f( )t) is depicted in three curves indicating how the surface resistance decreases relative to changes in temperature and treatment of the plastic shield with bromine for 12 hours. Curve I indicates treatment at 15 C., curve 2 same at 30 C. and curve 3 the condition of an untreated plastic. Analogous relationships are true for the types of plastic mentioned elsewhere in the specification. The table of FIG. 6 also provides information as to the efficacy of the antistatic treatment.

The process of the preach (Invention is particularly suitable for plastics which are employed in their glass-clear conditions, for example for glazing airplanes, instruments, etc., and whose optical properties are not significantly impaired by an antistatic treatment. Said plastics are, for instance, polystyrene, polyvinyl chloride, polyester, polyethylene and polycarbonate.

In accordance with the present invention, water vapor may be used, if necessary, in connection with the neutralization of the treated surfaces of the windshields.

The use of vapor is an optional process specifically for plastics which are difficult to brominate and which at room temperature can be brominated only to an economically unsatisfactory degree, if at all.

The diagram of FIG. 5 shows light absorption curves in relation to wavelength of untreated EEC plastic windshields x, of bromine-vapor treated EEC plastic windshields o and of EEC plastic windshields treated with bromine vapor under a high vacuum. The light permeability is indicated along the X-axis, the wavelength along the Y-axis. The diagram shows that short-wave light around 400 nm. is absorbed particularly intensively and is therefore suitable also for accelerating the reaction. The curves presented here apply only to allyl diglycol carbonate. With the aid of additional light treatment, the surface resistance can be lowered by one tenth power.

Subsequent to these process steps of the aftertreatment by virtue of which the excess bromine freed by the plastic is neutralized, it is expedient to soak the additionally treated plastic surfaces for several hours in order to eliminate the residual reaction products.

As residual reaction products, the following are obtained: halogen hydracid, water, and organic substitution and/or addition products of the plastics used.

The permeability to light of the windshields treated in accordance with the present invention, the diagram of FIG. 6 shows three curves which illustrate that the light is strongly absorbed only within the blue and violet ranges, but hardly within the normal visibility range. This graphic illustration proves that the process according to the present invention does not result in a significant impairment of the permeability to light or transparency of the treated windshields.

The RC 900 plastic mentioned in the tests of FIG. 6 is obtained by peroxyd polymerization of monomers of allyl diglycol carbonate The spatial bond with the macromolecule occurs on the C C double linkage. It is worth mentioning that no organic wetting-reactions occur quantitatively. Therefore, in the macromolecule remain in accordance with the degree of wetting occasional remaining double linkages. These C-C double linkages are capable to react in conjunction with various addition and oxydation reactions. The addition of bromine occurs generally radically stepwise often with superimpositions of these processes.

In accordance with the present invention aromatic and aliphatic amines, respectively, for example diethamolamine, are used for the neutralization of the treated surfaces of the windshields. They are employed preferably in aqueous solutions and at elevated temperatures.

The addition of a considerable amount of bromine causes a chain reaction. It occurs predominantly in the gaseous phase and is advanced generally by light or additions of radical starter mixtures in accordance with the following 15:1 Br-Br Br. Br.

Predominantly the brominating process occurs in polar solvents such as for instance in cooled acetic acid as well as in the presence of catalysts, as per following equations:

The neutralization is a necessary process step designed to reestablish the stability of the plastic and to eliminate excess bromine. It is possible, if desired, to complement the neutralization with a correspondingly long watering, i.e., rinsing of the plastic.

For purposes of the neutralization, the amines are preferably employed in the undiluted condition. The neutralization is carried out in every case of treatment until all free bromine has disappeared.

In FIG. 7 a treating device is shown for two airplane panes or Windshields, which shows the manner in which the saturation of the air takes place.

ln FIG. 7 an apparatus for carrying out the process of the invention is shown. The window shield to be treated itself is utilized as a wall of the treatment chamber. Other details of the apparatus will be obvious from the drawing to those skilled in this particular art.

The treatment of the windshields according to the process proposed by the present invention takes place at room temperature. The air is saturated with bromine vapor and its flow is directed over the windshield surfaces. The saturation of the air is achieved in that the air is passed in a closed cycle over liquid bromine in a storage container. The windshield may be treated with liquid bromine with diluents.

it should be understood that the foregoing disclosure relates only to preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples chosen herein for the purpose of the disclosure, which do not constitute departures from the spirit and scope of the invention as claimed.

I claim:

1. A process for treating a transparent plastic article such as a windshield of an airplane, comprising the steps of:

positioning a transparent plastic article in an atmosphere of air at room temperature;

directing a flow ofa fluid comprising bromine upon the surface of the transparent plastic article,

thus treating said surface by subjecting it to the action of said treatment being carried out at a temperature within the range of approximately 20 to 25 C. for a period of about 8 hours;

and subsequently neutralizing the surface in an aqueous composition or water vapor;

whereby the treatment steps render an antistatic permanent coating to the surface.

2. The process of claim 1. wherein the step of neutralizing the said treated surface is performed with aromatic amines.

3. The process of claim 2, further including the step of ex posing said surface during the treatment with aromatic amines under the influence of heat.

4. The process of claim 1, wherein the step of neutralizing the said treated surface is performed with diethamolamine.

5. The process of claim 1. wherein the step of neutralizing the said treated surface is performed with aliphatic amines.

6. The process of claim 5, further including the step of exposing the said surface during the treatment with aliphatic amines under the influence of heat.

I! i i i 

2. The process of claim 1, wherein the step of neutralizing the said treated surface is performed with aromatic amines.
 3. The process of claim 2, further including the step of exposing said surface during the treatment with aromatic amines under the influence of heat.
 4. The process of claim 1, wherein the step of neutralizing the said treated surface is performed with diethamolamine.
 5. The process of claim 1, wherein the step of neutralizing the said treated surface is performed with aliphatic amines.
 6. The process of claim 5, further including the step of exposing the said surface during the treatment with aliphatic amines under the influence of heat. 